Warp Drive Breakthrough

NIck Porcino writes "Warp drive one step closer to reality! From the abstract: A spacetime is presented for which the total negative mass needed is only the order of grams, accompanied by a negligible amoung of positive energy. This constitutes a reduction of the absolute value of the energy by 65 orders of magnitude. The new geometry satisfies the quantum inequality concerning WEC [Weak Energy Condition] violations and exhibits the same advantages as the original Alcubierre spacetime. Read it here. The two big problems to be resolved are 1) how do you get an object inside a warp bubble? 2) What happens to the object when the warp bubble collapses? "

Re:Negative Mass/Energy?

Her's how the Casimir effect works:

• Metal conducts electricity. Therefore, electromagnetic radiation at the surface of a piece of metal has zero electric field; otherwise the electrons in the metal would flow. (Of course if the frequency is high enough, the electrons can't keep up, and the metal becomes "transparent" to those fields. In other words, metal blocks radio waves, but is semi-transparent/semi-opaque to x-rays, and very transparent to gamma rays.
• A pair of parallel metal plates can have a standing wave electromagnetic field between them, much like pipe organs have standing air waves, or plucked guitar strings are a standing wave, and have a node at the bridge and the nut. When done with radio waves, you have what is commonly called "radar cavities", and indeed all of microwave & radar is based on this principle.
• Quantum space is filled with "zero-point" fluctuations in the electromagnetic field. These are basically electromagnetic waves that zip into existance for brief periods of time, and then cancel each other out again. When they occur between a pair of metal plates, these "unreal" quantum fluctions *must* have zero electric field on the metal plates, else the electrons would move.
• The pair of metal plates thus limit the types of virtual fields between them, resulting in a very weak attraction proportional to the distance between them taken to the fifth power. As someone mentioned, this effect was actually measured in th 1920's (?) and is almost simple enough to use a undergrad/grad school lab experiment.
• The theoretical interpretation is that the field between the plates has less than the average, i.e. less than zero amount of energy between them; i.e. since work=force x distance, and the force is attractive, the work (energy) must be negative.

So what do we have? We need to find a pair of very good conductors, made out of something much much smaller than atoms, and hold them a few hundred planck lengths apart from each other. The negative energy in between them should be enough to satisfy that needed in the theoretical paper.

BTW, a planck length is *very* small -- 10^-43 meters if I remeber right. Like a few *zillion* times smaller than an atom.

Re:Negative Mass/Energy?

I read something in Analog a few years back about
how running high frequency alternating current
through large capacitors causes their mass to
vary sinusoidally at about twice the frequency
of the current (and the amplitude of the
variations is proportional to the frequency).
(And I thought if you did this, the capacitor
would just get hot.)
I don't remember what this was called or who
discovered it; it has
something to do with Mach's Law. The effect
was supposed to have been observed, and
vanishingly small. But

1. Piezoelectric crystal can be made to expand
and contract with another alternating current.
The idea is, push on the capacitors when they
have low mass, and pull on them when they have
high mass. The resulting machine should be able
to float in mid-air or even accelerate, if the
amplitude of the effect can be made high enough.

2. The amplitude of the variation can (maybe) be
greater than the total mass of the capacitors,
leading to brief repeating periods of negative
mass. Don't think they last long enough to make
a very good warp drive, though...

Anybody care to burn up some capacitors and
test this?

--edkiser

Time Travel and FTL

First thing: If you want to read how traveling back in time to meet your former self might actually work, you MUST, *MUST* read "The Fabric of Reality" by by David Deutch.

He explains for the first time in any place, in a simple thought experiment, how such contradictions get resolved. He uses the language of recursive computing and turing machines, not physics, so you will be quite at home if you're are a CS major.


Secondly, FTL travel *doesn't* neccessarily lead to time travel.

As an example, I give you wormholes. Now, most people understand that all you have to do to cause wormholes to become time machines is accelerate one of the mouths until it has a different clock.

So for instance, let's say the entry point has a clock at 2pm, and the exit point has a clock of 1pm (because it is moving close to the speed of light and has a slower clock)

Now, if you bring those mouths of the wormhole within 30 minutes traveling distance of each other, you could enter the entrance at 2pm, arrive at the exit at 1pm, and fly back to the entrance and arrive at 1:30pm which is 30 minutes before you left. Then, you could stop yourself from going in.

However, there is a fundamental flaw in this argument. Matt Visser used relativistic quantum mechanics to prove that if you bring the mouths of the two wormholes close enough, virtual particles will form closed-timelike-loops *first*, the energy density of the space between the mouths will quickly diverge, and the wormholes will *close*

In other words, as soon as a closed-time-loop is close to being realized, radiation in the space diverges toward infinity rapidly, and the whole jumpgate collapses. :)

So, if we were talking about Babylon5 or StarTrek, there would be a fundamental law of the universe, which is wormholes can only be moved so close together. If you move them closer such that the travel time for light is less than the difference between their clocks, the wormholes will collapse.


Incidently, Hawking also proposed this, he called it the "Chronology Protection Conjecture", that the universe won't allow time loops to exist, and there would be an infinite radiation wall to travel through in any such loop.

There are many such theorems in physics, such as the "naked singularity" rule for black holes. Can a singularity exist without an event horizon, such that the rest of the universe could view it?
Probably not.

Re:Negative Mass/Energy?

In quantum tunnelling, the tunnelling particle has been considered to have negative energy, as it enters a region it doesnt have sufficent energy to enter (classically)

Some theorists postulate that it has "borrowed" energy from its surroundings, and has an energy debt, so has negative energy.

Putting negative energy into e=mc**2 gives interesting results for the mass, obviously.

The article was very interesting, but I dont think its been refereed yet, so I wouldnt get excited yet. It seems to rely on "Alcubierre Space" (which I've not seen defined) being either wrong, or adjustable. As its raining, and I should be revising for an exam tomorrow, I dont want to chase up references!

If, as is stated in the paper, microscopic warp bubbles are possible, would it not be possible to have a "warp foam", ie: a huge number of warp bubbles, and have them move together, that would avoid the size problem.

Layman's Terms

This paper is part of the ongoing abstract research into the possibility of travelling faster than light without breaking the laws of relativity. There are two leading proposals, usually referred in laymans terms as "Warp Drives" and "Wormholes".

The Warp Drive idea was first formalized (i.e. given all the math to show it should work, given sufficient engineering prowess) by M. Alcubierre, so it is sometimes called the Alcubierre Warp Drive. It has three big drawbacks: it requires an absurd amount of exotic energy and matter (some of which we don't yet know how to make), you can't see anything while Warping, and there is no theory on how to stop. This paper addresses the first problem, with the equations given, you need far less exotic energy and matter.

For some excellent laymans info on Faster Than Light issues, check out NASA's Warp Drive, When? [nasa.gov] site.

Negative Mass/Energy?

Have I missed something, or is negative mass and negative energy still in the "pure speculation" state -- the equations allow for it, and from a symmetry point of view it seems plausible, but last I heard we have no evidence for its existance, no theoretical way to produce any, etc.?

(Note: Negative mass is not anti-matter. Anti-matter has positive mass, and opposite charge/spin/other properties of "normal" matter. Matter plus anti-matter equals energy (which manifests as other postive-mass particles). Matter plus negative matter should equal nothing, zero, zip.)

Re:FTL

The problem is the mass increase. As you accelerate to the speed of light, you gain kinetic energy (naturally). We know that energy has mass. Solving the system of equasions (left as an exercise), we find that as v approaches c, mass approaches infinity. Thus, it takes an infinite amount of energy to actually reach lightspeed for ordinary matter (tachyons are another thing entirly).

So far, experimental evidence has matched the predicted values very nicely.

Re:Hmm...

Well, a class in quantum physics ain't going to help you. A class in general relativity might though.

The basic deal is that in the presence of extremely strong gravitational field movement in space along a certain path results in a movement in time. This is what is meant by the sentence: 'The idea is to start with flat spacetime, choose an arbitrary curve, and then deform spacetime in the immediate vicinity in such a way that the curve becomes a timelike geodisic, at the same time keeping most of spacetime Minkowskian'.

I remember (back as a physics undergraduate) learning a pretty cool visual explanation of this with little spacetime cones (the 45 degree edge of the cone representing light speed). The idea was to tip the cones over. Or something.

Anyway, Alcubierre's initial formulation of this space time can only be created by a ridiculously strong spinning gravitational field. I seem to recall something about a bloody huge sphere of material the density of a neutron star spinning so it's surface is going at 0.999c. Massive it was.

There are other problems with the Alcubierre geometry, namely basic things like electromagnetism gets buggered up, it requires lots of negative energy (think of negative pressure rather than straightforward energy) and anyway as soon as you start going faster than the speed of light it becomes physically impossible (with this geometry) to go faster than the speed of light. Go figure.

So this Belgian bloke has come up with a absolute wheeze: keep the surface area of the warp bubble you create really small but expand its volume to something you could reasonably fit a Volkswagen Polo into. Try this at home and you may run into the slight problem that volume usually increases to the 3/2 with area. Not a problem because this dude's a cosmologist, he's got all the paper and pencils he needs, and it always rains in Leuven so he's got nothing better to do. Check out eqn (4), it's a beauty.

Working through the maths he comes up with some numbers and - suprise - his new warp geometry requires much less negative energy than the Alcubierre geometry (which required rather more negative energy than the total positive energy in the universe, just to produce a warp bubble that could have been described as 'cramped and bit stuffy' by a vole). In fact using some sensible (i.e. off the top of his head) figures, he finds that you only need 3.4 grammes of negative energy.

The problems of where do you get the negative energy from, the massive densities involved and how do you get a macroscopic object into a bubble with infinitesimal surface area of course remain.

Your tax Belgian Francs at work people.

Hope this helps, Nick

Semi-ignorant question...

What happened to the other problems with FTL travel?

I'm thinking specifically here about the more slippery definition of "simultaneous" in special relativity, and it's consequences. Assume a ship that can:

a. Accelerate to any sublight speed (and thus any "normal" reference frame) arbitrarily fast.
b. Use "Warp Drive" to move between two points in space time faster than light.

That's all you need, and assumption a. is perfectly in accordance with physical laws (and technically plausible with some externally powered propulsion system).

Throw in the cute fact that for any two points in spacetime that are not in each other's light cones, there is an inertial frame of reference where those two points are simultaneous, and your ship can:

1. Warp 1000 light years away, simultaneous with the frame of reference of the solar system.
2. Accelerate to near light speed.
3. Warp back to earth, but 999 years before it left.

I wish I could link in a diagram of this... but go look in a physics textbook; it's a classic paradox meant to show why FTL travel is impossible.

I've never heard a good explanation of how Alcubierre's theory (not to mention whatever new concept has come up) deals with this.

Several schemes get around this paradox.

The simple fact that travelling backwards in time would allow me to kill my former self, thus preventing me from ever having gone back in time to do so, is a complete logical contradiction, causes me to not care even in the slightest about this or that new theory which suggest FTL travel.

It just ain't possible.

Not strictly true. All that your example shows is that you would not be able to kill your former self. Two of the several solutions that I've heard postulated are:

• Actions of time travellers must be consistent with observations.
  
  Under this system, you would certainly not be able to kill yourself, becuase you didn't (you survived to travel backwards in time, didn't you?). This physically corresponds to limiting (drastically) the number of possible events that can occur within a loop of spacetime that folds back on itself in the time direction. This in turn means that such loops are entropically very unfavourable, but they could still in principle occur if a greater increase in entropy happened elsewhere.
  
  
• Time travel is actually travel between multiple histories.
  
  This refers to the "multiple histories" interpretation of quantum dynamics. Under this system, when you flip a coin, it lands on both sides - just in different universes. What actually happens is that all possible ways for a probability waveform to collapse happen, in different universes. If you travel back in time, you arrive in another universe, that looks a lot like the one you remember from that time - but in which a time traveller spontaneously appeared and killed the person who would have been you in your universe. This system doesn't impose entropic limits, but how exactly you travel between parallel universes is left as an exercise.
  
  

Both of these systems avoid the paradox that you menion.

Re:Negative Mass/Energy? -Woodward's work

Well, there's Woodward's work. Basically, as a result of Mach's principle, it predicts a transient mass fluctuation in an LRC circuit.
It could be the "impulse engine" of ST fame, or the hover cars off the Jetsons...

(Just maybe, it could also provide a large enough mass fluctuation for more exotic uses, like temporary wormhole stabilisation...)

NB. IANAP (I am not a Physicist (...and boy, does it show...))

Woodward carried out a test, which seemed to confirm the theory. However, an unforseen non-linear response in some of the experimental equipment casts doubt on the first results. Even if the fluctuations were a couple of orders of magnitude smaller than observed, it would still be a major breakthrough. NASA seems to think so too, and are, AFAIK, quietly working on a repeat test in their breakthrough propulsion labs...

Anyway, the theory makes interesting reading.

Here's the relevant links:

chaos.fullerton.edu/Woodward.html [fullerton.edu]

www.inetarena.com/~noetic/pls/wo odward.html [inetarena.com]

Re:** DEAD STUPIDITY **

Actually, you're wrong on both counts.

1) You _can_ go faster than the speed of light, just not directly. You can't just turn the engines of a spaceship on "high," you have to skip over some of the space you're travelling through, and your _effective_ speed jumps past the speed of light. Both wormholes and "spacefolding" technologies - both of which are theoretically proven - would enable one to do this.

2) Yes, you can. In fact, we know how to do it today. The problem is, it takes an astronomically large amount of energy. It requires a wormhole in order to achieve it. You take one end of the wormhole and take it on a tour of the solar system at _relativistic_ speeds. You keep the other one stationary. Due to the time dilation, time passes for one a lot slower than it does for the other. Since one end of the wormhole has experienced less passage of time than the other, one end resides in the past, and one resides in the future. Then you can freely travel backwards and fowards through time via the wormhole.

There are other ways to travel backwards and forwards through time, but most are terribly implausible (e.g., infinitely long rotating cylinders spinning at relativistic speeds - I don't understand the full complexities of that particular process). And all have been discovered as parts of solutions to Einstein's equations, which have very little to do with quantum theory. So even assuming only relativity applies, you're still hosed.

Re:Negative Mass/Energy?

It's been demonstrated - the article even mentions the demonstration.

It's called the Casimir effect, and is based on the idea of virtual particles. Spacetime isn't flat - it's teeming with zillions of virtual particles that pop in and out almost instantaneously. Their existence is so short that it doesn't really matter much. However, an Italian scientist named Casimir theorized that if you took two uncharged metal plates and put them close together, they would attract each other via the net force of all these virtual particles.

A few years later (IIRC, mid 1920s), when somebody actually _tried_ this, sure enough they detected a net attractive force. As science progressed, it was determined that this attractive force is based on negative energy. Negative energy is one of the driving forces behind wormholes. In order to make a stable wormhole, you need "exotic matter" - a form of matter that has an average negative energy density. Nobody's ever seen exotic matter, but no equation or physical process has been seen or discovered yet that would rule out its existence.

Negative energy/virtual particles are also the process by which black holes give off radiation (yes, THEY DO RADIATE). If a black hole gives off more matter than they consume, they will shrink and eventually explode.

Not the Star Trek Universe it used to be

The energy that would be required for warp travel is irrelevent; energy is abundant at this time in the universe. (And worse come to worst, we sacrifice some matter.) Much of the physics we are dealing with is not conventional, and we will soon see a new relevation to change the entire perspective on the reality surrounding us. Warp drives, so cliche as that may be, can exist. Indeed, it is likely that they do. Just to throw you for a loop, it is possible and even probable that the entire universe is composed of a single electron in a parallel time frame for each instance (near infinite). Interesting, no? I say this because a positron, the electron's positive energitic counterpart, is mathematically described as an electron travelling back in time (i.e. negative time). Still, much work is to be done on this yet. The reality constraining us is not what it used to be. We should not forget what we have overcome, lest we fail to overcome the barriers before us now.

Re:** DEAD STUPIDITY **

Not only is faster than light travel possible, but I believe it has been demonstrated.

Information travels faster than light. (because information doesn't actually travel, for a normal definition of that word) Would someone with a heavier physics background please correct me here? I'm pulling this from memory:

Two particles can be bonded such that their collective spin state is always 0. knowledge (or lack thereof) of a particle's spin state is information. once these particles are bonded, the space seperating them is irrelevant. they can be next to each other or on opposite ends of the universe, and as soon as you change (observe) the spin state of one, the spin state of the other *instantly* becomes defined. the information travels without actually entering the space seperating the particles, which means that it isn't subject to the usual limitations placed on physical objects (namely a ~186,202 miles/sec speed limit).

i'm not sure how modern physics handles this. i believe einstein rejected it, but i think it's actually been experimentally confirmed in the past several years. you could incorporate yet another dimension into your conception of existance (5? 6? n?).

the curious part is how closely this resembles what mystics have been saying for millenia: space is an illusion.

another curious side effect of this is that the speed of light (in very much simplified laymans terms) seperates the "past" from the "future" and keeps them both out of the ever-present "present" (be here now). if you allow for faster than light travel, the chain of causality as we know it must be abandoned. the past and the future get all mixed up, and you have cause following effect etc.

i will cease my rambling now and get back to work :)

Re:Time travel (backwards)

Sometimes a paradox means that you don't understand all the facts. Other times, it means that you are simply not on enough hallucinagens. I suggest that the latter is the case here. The paradox only exists because we want to use our concept of time in a realm where we break the laws of our concept of time.

If I enter a time machine in 1999, go back to 1979, then kill the "other me" in 1989, then the "paradox" is that I cannot exist in time 1999 to do these things.

To an observer alive during all this time, they will see one of me until 1979, then sees my evil twin materialize for some unknown reason in 1979. Between 1979 and 1989, the observer sees both myself and "my evil twin" (who is actually myself, but may as well not be). After time 1989, the non-time-traveling me is in a pine box, while the evil twin is walking around.

From this observer's perspective, nothing of particular importance occurs in 1999. Nobody enters the time machine. The fact that my evil twin remembers a particular event in 1999 is irrelevant. It is irrelevant because 1999 is no longer what we think.

To those of us unfamiliar with time travel (I'll assume that's all of us, save the Gallifreyan contingent), 1999 is a fixed series of events. Or at least, the first five months of it is a fixed series of events--we don't remember the other seven months, because "they haven't happened yet". We have a one-to-one correlation between personal time and wall time. That is, we've already experienced "April 1999", and never expect to experience it again.

To my "evil twin", what we call "April 1999" has a many-to-one correlation with his own memory. He can go through April as many times as you can walk through a revolving door.

To the third-party observer, time travel didn't happen. Somebody shows up out of nowhere in 1979 (surely weird, but no paradox). He kills someone who looks like him in 1989, and lives past 1999 and well into the next century. No time travel, no paradox.

So who sees the paradox? The time traveler sees no paradox. Non-time-travelers see no paradox. The only way to see a paradox here is to exist outside of time. The only one I know like that is God Himself, and I don't think that He will get thrown by somebody dinking with a knife and a time machine.

Remember the Bart Simpson correlary to Shrodinger's Cat: "I didn't do it, nobody saw me do it, you can't prove anything". Since nobody can get both the precice position and the precice velocity of a particle, it is arguable that they do not exist. If no observer can record the phenomenon, it didn't happen. Since nobody can witness the paradox, it doesn't exist.

Note: I was kidding about the hallucinogens. If you need to stretch your mind in those sorts of directions, just stay away for four days straight. It works for me ;^>

Re:observer-based math!=relativity

I'm afraid you seem to have misunderstood the principle of relativity. There is no "REAL velocity". The whole point of relativity (at least, where it got its name from) was that it doesn't matter at all which observer you consider.

Of course, your speed will depend on the observer, just because it is defined relative to the observer. But the physics (i.e. what actually happens) is independent of the observer. In your example of a tree and an observer falling in the woods, the observer would certainly see that the tree is stationary, but the ground would seem to be travelling at a very disconcerting speed!

FTL

Okay, i'm no physics major.. but i try to keep current and have read enough to consider myself at the very least a knowledgable layman (yeah, i know the whole thing about a little knowledge being dangerous) and i cant say that i understand why exactly FTL travel is so impossible. I mean, why is 300,000km/s such a fundamental barrier? Okay, objects travelling anywhere near that velocity do behave oddly as we view them.. but who says that's so important? so the math says objects shouldnt exceed that speed without doing x y and z.. 100 years ago the math said a whole lot of things we know are patently false. *cough cough ether cough cough*

Now here's my take on it: relativity says that we cant exceed X m/s without having the rate we move through time change. So then in order to calculate exactly how fast you're moving, you have to do one of two things: calculate your base movement rate from an exact zero state an include your movement across the planetary surface, the revolutionary speed of the planet, speed of planet around the sun, speed of sun around galactic core, speed of galaxy in direction X (not to mention possible rotation of galaxy around unknown object(s) etc) or, the approach normally taken: ignore it. So far as i can tell from what i've read, relativity uses observer-based velocity. If your REAL velocity is 290,000km/s but the guy watching you sees you travel at 60 km/h.. according to relativity, you're doing 60 km/h. Now perhaps it's just me.. but this seems just a little silly. Why should who's watching alter everything? It's like the old 'if a tree falls in the woods and nobody's around, does it make a sound?' the obvious answer being 'yes'. Afterall, falling trees always make noise.. why would they stop? So then according to relativity, if a tree falls in the woods, and the only person around is falling too, it doesnt make a sound because, at the perspective of the observer, the tree never fell over. *shrug* i can understand collapsing waveforms and the uncertainty principle, but observer-based math just doesnt make any sense to me.
Dreamweaver

unverified

Keep in mind that xxx.lanl.gov (where the paper is posted) is not a refereed journal. This paper
may not have been subjected to any peer review, so it's contents should be taken accordingly. Many times serious corrections or withdrawals are made to this pre-print archive. It would probably be better to not publicize something like this until it has been read be many specialists.